Shell Utilities

The shell utilities implement a number of shell commands you can use interactively or in shell scripts. Each utility program performs a specific task. The idea is that you can combine these commands in shell scripts to perform more complicated tasks.

Table 8-2 briefly describes each shell utility. You can try out some of these utilities by typing the program name at the shell prompt. Each program takes command-line options. You should first type man progname, where progname is the name of the utility, to learn more about the command-line options. Then try the utility with appropriate options.

Cross Ref

You encounter some of these shell utilities again in Chapter 24 in the section covering shell programming.

Table 8-2: GNU Shell Utilities
Program	Description
[	Evaluates an expression and returns zero if the result is true (same as test)
basename	Removes the path prefix from a given pathname
chroot	Changes the root directory
date	Prints or sets the system date and time
dirname	Removes the last level or filename from a given pathname
echo	Prints a line of text
env	Prints environment variables or runs a command with modified environment variables
expr	Evaluates expressions
factor	Prints prime factors of a number
false	Returns an unsuccessful exit status
groups	Prints the names of the groups to which a user belongs
hostid	Prints the numeric identifier for the host
id	Prints the real and effective user and group IDs
logname	Prints the current login name
nice	Runs a program with specified scheduling priority
nohup	Allows a command to continue running after the user logs out
pathchk	Checks whether filenames are valid and portable
pinky	Prints information about users. (This is similar to the finger program; in fact, the name pinky refers to a lightweight finger.)
printenv	Prints environment variables
printf	Formats and prints data
pwd	Prints the working (current) directory
seq	Prints numeric sequences
sleep	Suspends execution for a specified time
stty	Prints or changes terminal settings
su	Enables the user to adopt the ID of another user, or the super user (root)
tee	Sends output to multiple files
test	Evaluates an expression and returns zero if the result is true
true	Returns a successful exit status
tty	Prints the terminal name
uname	Prints system information
users	Prints current user names
who	Prints a list of all users currently logged in
whoami	Prints the user name for the current effective user ID
yes	Prints a string repeatedly until the process is killed